This application relates generally to apparatus and method for the automatic depalletization, grouping and stacking of block-like objects, for example, concrete blocks. Blocks of at least two different orientations are placed in each layer of the stack so that the resulting stack is properly integrated and "tied" for structural stack integrity. In a "tied" stack, each layer of subunits is adjacent to layers of differing block patterns, so that contiguous blocks within each layer are held together due to frictional forces exerted by overlapping blocks in adjacent layers.
In particular, this invention relates to apparatus and method which, if necessary, first rotates the blocks so that a solid face is directed upward, and then moves a supply of blocks to each of two independent grouping systems. Each grouping system independently supplies blocks, in a respectively corresponding one of the two angular orientations used in forming a tied stack, to a marshalling area wherein the layers of the stack are formed. The successively formed layers are then lifted and stacked onto one another. In this invention, the layers of the stack and the stack itself are preferably formed so as to minimize the movement of the blocks and the time needed to form the stack.
Automatic depalletizers and stackers for concrete blocks are known in the industry. Some of these stackers are equipped with grippers, with or without rotating gripper pads, which take blocks off the pallets and place them on grouping conveyor systems so that flats (i.e., stack layers) may be assembled. The conveyor system may be operated according to U.S. Pat. No. 3,625,375 to Johann Lingl, issued Dec. 7, 1971 so as to provide spacing between groups of blocks. In other systems, a gripper places blocks on a table from which they are pushed onto another table consisting of two plates which, as flats are accumulated, are separated so that spaces are provided in the flat for insertion of the tongues of a stacking gripper, which successively lifts the flats onto a stack. Neither of these prior systems permit tied stacking wherein the blocks within a particular layer has more than one orientation.
Systems are also known for producing tied stacks where single rows of blocks are placed onto a conveyor system on which they are rotated so that the proper face is upward and from which they are then pushed onto a series of turntables. Blocks are then raked off the turntables so as to form flats with blocks of each row of a flat being oriented differently than blocks in a preceding row. These machines, however, have a very low capacity, since the blocks have to be fed to the accumulating position single file, and because the turning of the blocks requires an additional operating step. A further system is known wherein a single row of blocks is fed into a machine which has turning mechanisms installed over a feed conveyor, which turn one, two, or several blocks in a row at the same time on the conveyor before they proceed into a stacking system. This system also does not permit high capacity processing since only a single row of blocks is fed into the system at a time and because turning requires an additional operating step.
In U.S. Pat. No. 3,625,375, supra, brick flats are set on a first grouping system consisting of two conveyors forming flats of different lengths, wherein every other flat proceeds into a pick-up area for stacking, while alternating flats are transferred with a rotating gripper to another parallel grouping system operating in a manner similar to the first one. In the second system the bricks are regrouped in a different angular orientation to form the alternate layers of the rectangular stacks. The described equipment does not handle headers and stretchers (i.e., blocks having different angular orientations) in the same layer.
A similar system provides for an additional gripper to feed the regrouped bricks from the second grouping system back onto the first grouping system, thus permitting the placement of headers and stretchers in the same layer. This system requires more equipment than the present invention and is therefore more expensive. Also, it is limited in capacity because of the necessity to alternately group layers on the first grouping system, transfer them to a second one, and then return the bricks to the first grouping system.